Proving grounds only affects healing, not regeneration. FoN is a regeneration effect.

95% sure. Just pop a health potion to check, as that's regeneration.

I'm pretty sure, for simplicity's sake, Regen is treated as Healing over time (for effects like Spirit Visage) and Healing over team is treated as Regen (to give a number to how much you're healing per 5 seconds).

But Spirit Visage's effect specifically states that it affects "healing and regeneration", which would indicate that they are, in fact, two seperate things. But it's also possible that it's only there for clarification, and health regen DOES count as healing.

Also FoN's effect states that it "restores" health, whereas all regen-affecting effects (including its +40per5) say "regen" or "regenerate", so it's hard to tell which one it fits under.

I think we'll need one of Riot's coders to clarify this.

Again, pop a health potion, or buy a regrowth pendent. You shouldn't see the 20% penalty that's applied to healing.